A category of line monitors, such as power line monitors, includes the Ground Fault Circuit Interrupter (GFCI). To be commercially sold in the United States a GFCI should preferably be able to pass testing performed in accordance with Underwriter's Laboratory (UL) standards. For example, UL standard UL948 requires, among other things, that power be interrupted within a certain amount of time if a fault current level related to one of the electrical conductors (such as leakage current from one or more electrical conductors to ground) exceeds a specified threshold, and that power not be interrupted if a fault current is below another specified threshold. New techniques are needed to satisfy increasingly rigorous standards.